Electron discharge device



1954 s. w. LEFCOURT EI'AL I 2,693,397

ELECTRON DISCHARGE DEVICE Filed July 1, 1948 SILVER MflG/VES/UM .0 I u 1 a 1 I l 0 z a 4 5 6 7 a HOURS OF LIFE INVENTORS Sta/2Z6 11/. Lefi'c auri' FIE-4.- Haber Mayer Alto/hey United States Patent ELECTRON DISCHARGE DEVICE Stanley W. Lefcourt, New York, N. Y., and Robert Mayer,

Havertown, Pa., assignors to Sylvania Electric Products Inc., a corporation of Massachusetts Application July 1 1948, Serial No. 36,326

2 Claims. (Cl. 313-103) This invention relates to an electron discharge device more particularly to a device of this type which contains a secondary electron emitter and to the method of making such an emitter.

For one reason or another it has heretofore been considered necessary to mechanically attach the secondary electron emitter to a support structure which passes through the tube envelope. This type of structure was considered to be particularly necessary in a microwave dynatron in which the secondary emitter is spaced only a few thousandths of an inch from an oxide coated filament. A structure of this type is shown in the patent application filed by George D. ONeill on March 13, 1948, hearing Serial No. 14,807, now Patent No. 2,679,591.

In view of the two-piece structure, that is, the emitter support rod with the attached electron emitter, it was heretofore necessary to provide a threaded hole at the bottom of the emitter support rod, a thread at the top of the emitter-electrode, a wrench 'hole at the side of the emitter, a thread at the outer edge of the grid frame and a threaded inner edge at the grid shell. Since the presence of these features required special machining of each of the parts, the structure was quite expensive and did not lend itself to high production techniques.

Among the reasons that this type of structure was deemed necessary are the following: The electrode support rod, since it passes through the glass envelope, must be made of a material which will permit good glass-to- --rnetal seals and none of the base materials which had heretofore been used for making the secondary emitter electrodes was suitable for such use, that is, none of the materials would permit the obtaining of the desired high secondary emission characteristics. Furthermore, the silver magnesium alloy which had heretofore been used for this purpose and which was sensitized with cesium is extremely unstable at the high temperatures which would be developed in this region during the period in which the grid frame is sealed to the glass envelope.

An object of this invention is to provide a simplified and more economical structural design for electron discharge devices having an electron emitting electrode.

A further object of this invention is to provide a more stable secondary electron emitter which can be present within a glass envelope at the time glass scaling is carried out in its vicinity.

In accordance with our invention we have found that these and other objects and advantages can be achieved if the secondary emission electrode support rod is made of a nickel chrome iron alloy of the type described in Patent No. 2,284,151 issued to Walter E. Kingston in which the nickel content is 345%, the chromium content 3-15 and the metals of the group consisting of aluminum, zirconium, calcium .1 to 2%, and the balance substantially of iron.

The invention in its several aspects will be better understood from the following detailed description of the illustrative form of dynatron shown in the drawing.

Fig. 1 is a longitudinal section of a planar grid tube showing the improved simple structure,

Fig. 2 is an enlarged fragmentary longitudinal section of Fig. 1, and

Fig. 3 is an enlarged fragmentary longitudinal section showing the electron emitter attached to the old type support rod and Fig. 4 is a chart showing comparative life of two different dynodes.

A simple embodiment of the features of this invenice .tion is shown in Fig. 1 of the drawings wherein the rod 10 which passes through the glass envelope 12 and is sealed thereto at point 14 is the .secondary .emittingelectrode .or dynode. The base or face of the rod 10 being the sensitized surface 16, facing the oxide coated filament 30 with a screen grid 22 interposed therebetween. The rod 10 in this embodiment of our invention is made of the above-noted nickel chrome alloy which is referred to in the trade as Alloy No. 4 and is further sensitized with a secondary emission material 18.

The grid 22 illustrated in the drawings, is a planar mesh grid mounted on a grid frame 24 which passes through the glass envelope and is sealed thereto forming a skirt 26 on the outside of the tube envelope.

The primary emitter electrode shown in this embodiment of our invention is an oxide coated filament 30 mounted on a mica disc 32.

The fragmentary view of the relevant portions of the tube shown in Fig. 3 illustrate the prior art type design in which the electrode support rod 40 which passes through the envelope in the same manner shown in Fig. l is made of copper rod and the secondary emitter electrode itself is made of a silver magnesium alloy 42 which has been activated with a thin film of cesium 44 being deposited thereon. in view of the fact that the silver magnesium metal is not a good material for obtaining glass-to-metal seals, the electrode material is provided with a thread 46, which is adapted to fit into the thread hole 48 at the bottom of the electrode support 49 and, furthermore, since the electron emitting material is not stable in the presence of heat when sealing the glass envelope to the grid support, a special grid frame 50 with a threaded outer edge 52 is provided to fit into and be adaptable for threading into the inner edge of the grid shell 54. With the aid of these features it was thereby possible to first seal the secondary emitter electrode sup port through and to the glass envelope thereupon seal the envelope to the grid shell 54 after which the secondary electrode or dynode 42 is screwed into the electrode support rod by means of the thread on top of the electrode and the threaded hole on the bottom of the electrode, special wrench holes, 56 and 58 being provided in the electrode and the electrode support for this purpose. After the electrode had been properly fastened to the electrode support rod it was then possible to thread the grid frame, with the grid, into place. Special wrench holes'60 and 62 were also provided in the grid frame for this purpose.

By comparison of the two embodiments shown in the drawings, it can readily be seen that the embodiment illustrated in Fig. 1 is a much simpler structure and much more economical to produce. The fact that the emitter support rod forms a base for the secondary emission surface while simultaneously serving as the material to which glass is directly sealed eliminates the need for threading a hole at the bottom of the electrode support rod, threading the top of the separate small electrode, providing wrench holes at the side of the electrode and the support rod, threading the outer edge of the grid frame and threading the inner edge of the grid shell as well as supplying wrench holes in order that these two may be properly fastened together.

The No. 4 alloy, when used as shown, readily lends itself to sensitization by coating with secondary emission materials such as the alkali metals and the alkali earth metals. Particularly good results have been obtained when thin deposits of the oxides of these metals such as for example barium oxide, cesium oxide and cesium silver oxide have been used.

Not only has the No. 4 alloy proven to be a good material for use as a secondary emitting electrode material because of its good glass-to-metal sealing properties but it has also proven itself to be an excellent medium for sensitization with the alkaline earth or alkali metals. The surfaces so produced have been found to be extremely stable even in the presence of heat such as is encountered in those areas in which glass-to-metal seals are being made. Furthermore, surfaces sensitized in this manner have been found to give long life secondary emitters, even in those cases in which the emitter surface faces the oxide-coated filament and is not provided with a shield therebetween. In those cases in which it has heretofore been deemed necessary to have this secondary emitter surface close to the oxide filament it had been deemed a necessary adjunct that the secondary emitter life would be very short for example when tubes of the type as shown in Fig. l were made with the secondary emitter being cesium on silver magnesium the tube life was approximately 1 hour. However, since using No. 4 alloy as the base metal for sensitization with the thin deposits of the alkali metals and the alkali earth metals tube life has been increased. This is clearly shown in Fig. 4 in which the secondary emission ratio is charted against hours of life. In the illustration there shown the life of a cesium activated silver magnesium dynode is compared with the life of a No. 4 alloy dynode sensitized with barium oxide. The ratio of 1.5 is approximately the minimum usable value. It has further been found that the life of the dynode can be further increased without deleteriously afiecting its heat stable characteristics by sensitizing its surface with a mixture of cesium oxide and silver oxide. Dynodes having a life of two hundred hours when used in electron discharge devices of the type illustrated have been made and tested.

There are numerous methods by means of which thin deposits of the sensitizing material can be applied to the No. 4 alloy. A preferred example of such method being one in which an alkali metal compound such as cesium carbonate together with silver oxide is applied to the back of the getter in such position that the applied material upon vaporization will deposit upon the secondary electrode surface. This can often be advantageously coupled with a later bombardment of the grid to vaporize and drive off any of the sensitizing compound deposited thereon which revaporized compound may be redeposit on the secondary electrode surface. During operation of the electron discharge device which consists primarily of a filamentary cathode 30, an electrode 22 termed a grid and conveniently formed of wire mesh and a secondary-emissive electrode 16 herein termed a dynode, the grid accelerates the primary electron stream from the cathode to the dynode and also serves to collect the secondary electrons emitted by the dynode. If a fixed potential difference is established between cathode 30 and grid 22 to make the latter positive, and various static voltages are applied to dynode 16, the dynode current will be observed to increase gradually. After a certain point the dynode current will decrease almost linearly to a minimum, even reversing direction, and thereafter it will increase again. This may be understood by recognizing the composite character of the dynode current, including a part of the primary electron emission leaving cathode 30 which penetrates the interstices of grid 22 to impinge upon the dynode 16 and,

subtracted from this, is the secondary electron emission resulting from this primary-electron bombardment. Between certain limits, the decrease of current drawn by the dynode and finally, the, true reversal of current in the dynode as the dynode potential is increased shows the dynatron to be a negative resistance device. This negative resistance characteristic can be variously used, as for amplifying, for detecting, and for modulating.

While the above description and the drawings submitted herewith disclose preferred and practical embodiments of the electron discharge device of this invention it will be understood by those skilled in the art, that the specific details of construction and arrangement of parts as shown and described are by way of illustration and are not to be construed as limiting the scope of the invention.

What is claimed is:

1. In an electron discharge device a glass envelope, a nickel iron chromium alloy rod extending through said glass, said alloy having a nickel content of 38-45%, a chromium content of 315%, .1 to 2% of the metals selected from the group consisting of aluminum, zirconium and calcium and the balance substantially iron, said rod having a sensitized surface formed by a thin deposit of a cesium oxide, silver oxide complex thereon, an oxide coated filament spaced directly opposite said sensitized surface with a planar grid therebetween.

2. In an electron discharge device, a glass envelope, a nickel-iron, chromium alloy rod extending through said glass envelope, said alloy having a nickel content of 38-45 percent, a chromium content of 3-15 percent, .l2 percent of the metal selected from the group consisting of aluminum, zirconium and calcium and the balance substantially iron, said rod having a sensitized surface formed by a thin deposit of the oxides of a metal selected from the group consisting of the alkali and alkaline earth metals thereon, and an oxide coated filament spaced directly opposite said sensitized surface with a planar grid therebetween.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,284,151 Kingston May 26, 1942 2,353,743 McArthur July 18, 1944 2,390,701 Ferris Dec. 11, 1945 

1. IN AN ELECTRON DISCHARGE DEVICE A GLASS ENVELOPE, A NICKEL IRON CHROMIUM ALLOY ROD EXTENDING THROUGH SAID GLASS, SAID ALLOY HAVING A NICKEL CONTENT OF 38-45%, A CHROMIUM CONTENT OF 3-15%, .1 TO 2% OF THE METALS SELECTED FROM THE GROUP CONSISTING OF ALUMINUM, ZIRCONIUM AND CALCIUM AND THE BALANCE SUBSTANTIALLY IRON, SAID ROD HAVING A SENSITIZED SURFACE FORMED BY A THIN DEPOSIT OF A CESIUM OXIDE, SILVER OXIDE COMPLEX THEREON, AN OXIDE COATED FILAMENT SPACED DIRECTLY OPPOSITE SAID SENSITIZED SURFACE WITH A PLANAR GRID THEREBETWEEN. 